Federal regulators moved Friday to suspend trading in three little-known companies run by a former University of Oregon football star over concerns about their investments in cryptocurrency.

The companies are all penny stocks that trade over the counter: PDX Partners, Cherubim Interests and Victura Construction Group. All list their chief executive as Patrick J. Johnson, who played for the Oregon Ducks and the Baltimore Ravens in the NFL.

"We're not in the crypto space at all," Johnson said by phone Friday. He said the U.S. Securities and Exchange Commission has not asked for any specific information from him but said he would cooperate with any requests.

PDX Partners makes iPhone apps, according to Johnson. Last month, his company said it had acquired $350 million in assets belonging to a private equity firm called NVC Fund Holding Trust, whose portfolio includes "cryptocurrency and business financial services."

Johnson said Friday that PDX Partners had acquired unspecified "trust units" from NVC, but he declined to describe the underlying assets those units represent and suggested instead reviewing SEC filings for another of his companies, Cherubim.

Cherubim bills itself as a specialist in "alternative construction projects." The SEC said Friday that Cherubim had recently announced the financing for "an initial coin offering," a term that describes raising funds for cryptocurrency ventures.

Cryptocurrency has become a hot investment as investors speculate about the potential value of digital currencies such as Bitcoin. Some companies, such as KODAK, have promoted cryptocurrency investments in hopes of reviving their flagging businesses.

However, the price of cryptocurrencies has been highly erratic, and many economists are skeptical about their underlying value.

The SEC said it acted against PDX Partners "because of concerns regarding the accuracy and adequacy of information in the marketplace about, among other things, the nature of the company's business operations and the value of its assets." It halted trading for 10 days, but could extend the suspension.

Shares in PDX Partners were trading at one-fifth of a cent, or 0.2 cents, on Jan. 4, the day it announced its arrangement with NVC. By Jan. 29, the stock had climbed to 0.69 of a penny - a 245 percent increase. (The stock has since fallen to 0.45 of a cent, still more than double where it was on Jan. 4.)

Shares in Cherubim closed Thursday at 0.003 of a cent before the SEC halted trading. Shares in Victura closed at two-tenths of a penny.

"This is a reminder that investors should give heightened scrutiny to penny stock companies that have switched their focus to the latest business trend, such as cryptocurrency, blockchain technology, or initial coin offerings," Michele Wein Layne, director of the SEC's office in Los Angeles, said in a written statement.

The SEC warned investors last summer to watch for companies that announce cryptocurrency activities in an attempt to boost their share price.

Correction: This article has been corrected to reflect that PDX Partners claimed it had acquired $350 million in assets from NVC, not $350,000.